Process for producing acid oils



Oct. 25, 1938.

B. s. GREENSFZLDER ET AL P ROCESS FOR PRODUCING ACID OILS Filed July 2l, 1936 ignara/pf- Vrac/ar Patented Oct. 25, 1938 UNITED STAT-Es PATENT OFFICE PROCESS FOR. PRODUCING ACID OILS Bernard Sutro Greensfelder, Martinez,l Monroe Edward Spag-ht, Long Beach, and Clyde Harold Britten, Wilmington, Calif., assignors to Shell Development Company, San Francisco, Calif., a

corporation of Delaware Application .'uiy 21, 1936, Serial No. 91,684

8 Claims.

This invention relates to the production of acid oils, and is directed particularly to the extraction of hydroxyaromatic compounds from cracked gasoline distillates.

The term acid oils, oxyorganic acidic substances, dominantly of hydroxy aromatic as herein used, refers to consisting preccmpounds and occurringl principally in cracked hydrocarbon oils, and does not include organic acids produced by the interaction of mineral acids and organic compounds.

Suchl acid oils are useful as selective carbon distillates. It is another vide a method for reiining crude acid oils obtained 'by the extraction of mineral oils.

purpose to pron cidental to the complete extraction of acid oils, partially refined distillates are produced, which are easily sweetened, cause little contamination and permit low consumption of treating agents subsequently used to refine these distillates.

In the past it has been customary to remove acidic components from mineral oils by treatment with caustic solutions oi the approximate strength of about 5 to 20 B. Most of the acid oils are weak acids, i. e. they have low dissociation constants and. in consequence, aqueous solutions of caustic extract the acid oils incompletely. It has been attempted to overcome this diiiioulty by treating acid oil-bearing anhydrous caustic. or passing the distillates with distillate vapors through molten caustic, or distilling over caustic,

etc. These methods, although more or less complete extraction resulting in a of the acid oils,

have the disadvantage of being wasteful because of incomplete utilization of the caustic, and moreover,` they are quite awkward reasons. i

for mechanical Our invention consists essentially of treating the mineral oil distillate containing acid oils with an amount of aqueous caustic solution of 3050% concentration or aqueous acid oil soap solution containing free caustic Sil-% caustic used being very slightly of the combined actions of the a more or less complete removal and being equivalent to a caustic solution, the amount of free in excess of the of the distillate.

soap and alkali, of acid oils from mineral oils can be achieved with practically no waste of unusedcaustic. The acid oils which are extracted with this aqueous soap solution are usually highly contaminated with impurities such as sulfur compounds, which render the acid oil 5 malodorous and unstable; to produce a better marketable product we have invented a refining process comprising a strong oxidation ofl the acid oil while in the caustic solution, followed by a solvent extraction.

We have observed that cracked distillate fractions boiling below about C. are practically free from acid oils; fractions boiling between ISO- C. contain very4 small amounts only,

while the fractions boiling above 175 C. contain 15` varying amounts of acid oils. For example, a cracked gasoline distillate of an acid oil content of .4% was fractionally distilled. The fraction boiling below 150 C. contained less than .02% acid oil; the fraction boiling from 150-175 C. 20 contained about .12%, and the fraction boiling between 175-225 C. contained 1.5% acid oils, concentration peaks of 1.8% and 2.6% appearing in the fractions boiling from 183-186 C. and 201-207 C. respectively. Fractions boiling sub- 25 stantially above 225 C. such as gas oil fractions boiling above about 300 C. usually are deficient in acid oils. In accordance with the above mentioned observation we have devised an efficient method for 3o obtaining highly concentrated acid oils from cracked distillates byfractionally distilling such distillate to separate at least one fraction boiling below .about 175 C. and subjecting the higher Y boiling fraction or parts thereof boiling below 35 300 C. or preferably below 225 C. to the extraction with an aqueous caustic solution of B0-50% concentration or an equivalent acid oil soap solution containing free caustic. The

separation of the excessively light and heavy 40.

recovery of acid oils which are relatively little 50 contaminated withl sulfur compounds, reduced losses of distillate, and greater ease of handling. The caustic extraction is preferably carried out at ordinary temperatures lof the order of 10-40 C., although higher or lower tempera- 55 tures substantially below the boiling temperatures of the reactants may be employed. While any alkali metal hydroxide is suitable for our purposes, in practice, sodium and potassium hydroxides only are the most likely to' be used, lithium, cesium, and rubidium being too expensive. The concentration of the caustic solution must be held between the limits of 30-50% for the following reasons: Alkali solutions of concentrations less than 30% do not form soap solutions of sumcient concentration to exert a substantial solvent action on acid oils, the result being incomplete removal of acid oils from distillates; and solutions of concentrations higher than 50% are so viscous that they are difficult to handie, and frequently result in obstinate emulsions. The effect of alkali concentrations on the emciency of acid oil extraction data in the table below:

Distribution of acid oils .between cracked distillate and sodium hydroxide solutions Toticll milloi Voli. loient 80 B0 0 D Conc. of NaOH solution systemo rma] treated mib NaO used late 40 Be (35% NaOH) gi 1.10 u Be (19% Neon) g .9e 1.10 55 `In the above tabulation it may be seen that an-equivalent amount of B. sodium hydroxide solution, that is, one in which the total number mols of acid oil in the system per mol of caustic equals one, removes acid oils from the distillate to a greater extent than a 100% excess of a 25 B. sodium hydroxide solution. On the other hand, it appears that if more than a molal equivalent oi' acid oil is treated with a caustic solution of a strength within the optimum range, a substantial amount of acid oil remains in the distillate. For these reasons, we prefer to regulate the ratio o1' distillate a'nd caustic solution of the requisite strength so as to produce soap solutions containing at least .80 and not more than about .98 mols o1 acid oil per mol of caustic. Under these conditions the extraction is substantially complete and very little caustic is unused. Y l

The minimum concentration of soap in the aqueous alkali hydroxide necessary to exert a markedly improved solvent action varies considerably with the type .of acid oil in the soap as well as in the distillate. It was observed that upon addition of relatively small amounts of soap acid oils to aqueous caustic 'of 30 to 50%, separates out until, upon further addition of acid oil to the caustic, a critical solubility point is reached where the concentration of the soap becomes such that a single homogeneous aqueous solution oi caustic in the soap is formed. We have found that the distribution of acid oils between the oil and aqueous phases becomes particularly favorable to the latter when the concentration of soap in this phase about equals or especially advantageous from exceeds that which is necessary for the complete dissolution of the aqueous caustic in the soap.

While. as hereinbeiore shown,`our process or acid oil' removal from hydrocarbon distillates is the point of view it also makes possible ftion extracted .19%

is illustrated by the the removal of certain types of acid oils which cannot be removed from the mineral oils by aqueous caustic alone, possibly because oi' their low solubility in aqueous caustic, except in the presence of a substantial amount of soap. For instance, a cracked gasoline was pretreated with 20 B. caustic solution, and the pretreated gasoline was then divided into two portions, one of which was treated with anl excess of 40 B. fresh caustic solution and the other with an equal amount of partially spent caustic solution containing about .80 mol of acid oil which originally had a strength of 40 B. The fresh soluacid oil from the distillate, whereas the partially spent one extracted .40%.

During the treatment with caustic containing soaps, impurities of the type oi' mercaptans are extracted from dlstillates jointly with acid oils. Acid oils liberated from the soaps by acidification are, therefore, malodorous and unstable and it, is very desirable to subject the acid oils to a refining treatment. We usually proceed by separating the spent caustic from the distillate and subjecting the spent caustic comprising essentially an alkaline reacting solution of soap to an oxidizing treatment in order to convert mercaptides lto disulildes, and then extracting the disulfldes Vwith a preferential solvent for organic disuliides, such as naphtha, pentanes, hexanes,

benzol, carbon-tetrachloride, dichlorethane, etc. 'Ihe oxidation reaction. is preferably carried out 'oxidizing reagents than those recited, to wit, po-

tassium permanganate, chromic acid, etc., are apt to destroy the acid oils, and, therefore, should not be used. The temperature of our oxidizing treatment is usually substantially atmospheric of the order oi.' 10 C. to 40 C. although somewhat elevated temperatures may beused to accelerate the reaction.

The oxidized soap solution is now ready for acidication to liberate acid oils. Acidiflcation is preferably carried out with inorganic acids, which must be more strongly acidic than the acid oils themselves. Strong acids such as hydrochloric acid, sulfuric acid, or weaker acids such as phosphoric acid, sulfur dioxide, carbon dioxide, hydrogen suliide, etc. may be used.

AIn a particular instance, a soap solution obtained lby extracting a distillate, boiling from 160 to 225 C. with a 40 B. caustic solution, and containing .98 molor acid oil per mol. of caustic was treated with 4% hydrogen peroxide by weight oi' the acid oil. Heat evolved during the reaction f and the mixturedarkened. The oxidized mixture was subsequently washed with benzol and acidified with dilute sulfuric acid. Acid oil was liberated and allowed to separate. 'I'his acid oil had a light color, phenolic odor, and a sulfur cona quantity oi' aqueous caustic solution or an acid oil soapsoluresulting soap solution are allowed to separate.

the soap solution containing a small amount of free caustic settling as the lower layer, whence it is withdrawn and transferred to a separate vessel for oxidation, extraction and subsequent acidication.

It is immaterial whether the aqueous caustic solution used in the treatment contains originally acid oil soaps or not, as long as the soap solution resulting from the treatment contains acid oil soap at least to the extent of the critical solubility point and some free alkali hydroxide.

In the continuous process a circulating stream of acid oil soap solution is maintained. Aqueous caustic is continuously introduced at one point of the circuit, and the resulting solution of soap and caustic is contacted with the necessary volume of distillate to convert substantially all of the newly added hydroxide to soap. After separation of the distillate an amountof the soap solution equivalent to the added caustic solution is withdrawn andthe remainder is circulated as described.

Referring now to the drawing, which represents a flow diagram of a continuous form of our process: Distillate vapors containing acid oil are introduced from a source not shown, through line I into fractionating tower 2, where they are separated into an overhead fraction boiling within gasoline boiling range and a heavier bottom fraction. The overhead fraction, after it passes through transfer line 3 is refractionated in fractionator 4 into overhead vapors boiling below about 175 C. which leave through vapor line 5,

and a bottom fraction containing acid oil, which passes through cooler 6 in line 1 to tank 8.

The bottom fraction from fractionator 2, which normally also contains acid oils, is cooled in cooler I0, situated in line 9, and proceeds to tank II. From tanks 8 and II acid oil containing distillates may be fed at separate times through lines 8 and II', respectively, to the caustic treating system which is as follows: Pump I2 picks up the oil from tanks or I I, and forces it, together with aqueous caustic solution from linel I1, through mixer I3 into separator I4. In separator III-treated oil and aqueous soap solution are separated, treated oil going to storage through top line I5 and soap solution being returned through bottom line I6 and lines I8 and I'I' to pump I2, to be mixed with further quantities of oil from tanks 8 or II. A portion of the soap solution is continuously withdrawn from the cycle, through line I9 into tank 23 and an equivalent amount of fresh caustic is introduced into line I'l from caustic tank 20, conveyed by pump 2l in line 22. Care must be taken that the ratio 'of freshly added caustic and acid oil containing distillate which jointly pass through the mixer I3 together withA a circulating soap solution is such that the soap solution after separation of the distillate in separator I4 contains some free alkali and acid oil at least to the extent of the critical solubility point and preferably between .8 and .98 mol. of acid per mol. of caustic.

The spent caustic comprising a soap solution in tank 23 is now forced by pump 24 together with an oxidizing reagent such as hydrogen peroxide, hypochlorite, etc., from tank 21 and line 28, through mixer 25 into extractor 3l, in which the oxidized caustic mixture is extracted with a suitable solvent for disuliides, such as naphtha.

The solvent, introduced through line 32, flows in an upward direction through extractor Il and is withdrawn through top line 33, while/'the caustic mixture entering through line 20 ilows downward and is transferred by pump 34 in line 35 through mixer 36 to separator 40, together with a suillcient amount of acid from tank 31 and line 38 to produce a slightly acidic mixture, whereby acid oils are liberated. The acidic mixture enters through line 39 into separator 40, where the liberated acidolls are separated from the acidic aqueous solution, treated acid oil being removed from top line Il and aqueous solution through bottom line 42.

We claim as our invention:

1. In the process of extracting acid oil from a mineral oil distillate containing same with an aqueous alkali metal hydroxide, whereby acid oils are caused to react with the hydroxide to produce a soap solution, the improvement comprising treating said liquid distillate with an amount of a liquid mixture consisting essentially of water, acid oil soap and free alkali metal hydroxide and being equivalent to an original aqueous alkali metal hydroxide solution of 30 to 50% concentraytion to neutralize a portion only of said free a1- kali metal hydroxide and to raise the acid oil soap content of the mixture at least to the critical solubility point of the soap above which the mixture forms a single phase, andseparating the treated distillate from the resulting aqueous soap solution.

2. In the process of extractingacid oil from a mineral oil distillate containing same with an aqueous alkali metal hydroxide, whereby acid oils are caused to react with the hydroxide to produce a soap solution, the improvement comprising treating said liquid distillate with an amount of a liquid mixture consisting essentially of water, acid oil soap and free alkali metal hydroxide and being equivalent to an originalaqueous alkali metal hydroxide solution of 30 to 50% concentration to neutralize a portion only of the free alkali metal hydroxide and to produce a solution in which the mol ratio of acid oil to alkali metal is between the limits of .80 to .98, and separating the treated distillate from the resulting aqueous soap solution.

3. In the process of extracting acid oil from a mineral oil distillate containing same with an aqueous alkali metal hydroxide, whereby acid oils are caused to react with the hydroxide to produce a soap solution, the improvement comprising fractionally distilling said distillate to produce a light fraction boiling substantially below 175C. and aheavier fraction, treating the heavier fraction with an amount of 'a liquid mixture consisting essentially of water, acid oil soap and free alkali metal hydroxide and being equivalent to an original aqueous alkali metal hydroxide solution of 30 to 50% concentration to neutralize -a portion only of said free alkali metal hydroxide and to raise the acid oil soap content of the mixture.'at least to the critical solubility point of the soap, above which the mixture forms a single phase, and separating the treated distillate from the resulting aqueous soap solution.

, 4. In the process of extracting acid oil from a lmineral oil distillate containing same with an f MM.-

and free alkali metal hydroxide and being equivalent to an original aqueous alkali metal hydroxide solution of 30 to 50% concentration to neutralize a portion only of said free alkali metal hydroxide and to raise the acid oil soap content of the mixture at least to the critical solubility point of the soap above which the mixture forms a single phase, and separating the treated distillate from the resulting aqueous soap solution.

5. A continuous process for the substantially complete recovery of acid oil from mineral oil containing acid oil, by extraction with an aqueous solution of alkali metal hydroxide whereby acid oil is caused to react with the alkali metal hydroxide to produce soap and water, comprisingccontinuously circulating an aqueous acid oil soapsolution which contains free alkali metal hydroxide and acid oil soap at least to the extent of its critical solubility point, said soap solution being equivalent to a 30 to 50% alkali metal hydroxide solution, continuously admixing a quantity of fresh aqueous alkali metal hydroxide solution of 30 to 50% concentration, continuously treating with the resulting aqueous mixture a volume of said mineral oil containing a quantity of acid oil absorbable in the said mixture which is suilicient to raise the acid oil soap content of the said mixture at least to the critical solubility point of the soap, above which the mixture forms a single phase, thereby converting the mixture to the aforementioned aqueous acid oil soap solution, separating the treated mineral oil from the aqueous acid oil soap solution, and continuously withdrawing an amount of the latter having the same alkali metal content as the said quantity of fresh aqueous alkali metal hydroxide.

6. A continuous process for the substantially complete recovery of acid oil from mineral oil containing acid oil, by extraction with an aqueous solution of alkali metal hydroxide whereby acid oil is caused to react with the alkali metal hydroxide to produce soap and water, comprising continuously circulating an aqueous acid oil soap solution in which the molal ratio of acid oil to alkali metal hydroxide is not less than .80 and not more than .98, said soap solution being equivalent to a 30 to 50% alkali metal hydroxide solution, continuously admixing a quantity of fresh aqueous alkali metal hydroxide solution of 40,. to 50% concentration, continuously treating with the resulting aqueous mixture a volume of said mineral oil containing a quantity of acid oil absorbable in the said mixture which is approximately equivalent tothe said quantity of fresh aqueous alkali hydroxide, thereby converting said mixture to the aforementioned aqueous acid oil soap solution, separating the treated mineral oil from the aqueous acid oil soap solution, and continuously withdrawing an amount of the latter having the same alkali metal content as the said quantity of fresh aqueous alkali metal hydroxide.

7. In the process of producing stable acid oil from a mineral distillate containing acid oil and acidic sulfur compounds, the steps comprising treating said distillate with aqueous acid oil soap solution containing free alkali metal hydroxide and being equivalent to an aqueous alkali metal hydroxide solution of 30 to 50% concentration under conditions to react acid oil and acidic sulfur compounds with the alkali metal hydroxide and to form a soap solution containing acid oils and sulfur compounds at least to the extent of the critical solubility point of the soap, separating the treated distillate from the resulting soap solution, subjecting the 'latter to an oxidizing treatment suiiiciently vstrong to convert alkali metal mercaptides to disulfides but insufilciently strong to oxidize a substantial amount of acid oils, washing the oxidized soap solution with a solvent for disuliides, acidifying the washed soap solution to liberate acid oil and separating the liberated acid oil from the acidied solution.

8. The process of claim 7 in which the oxidizing treatment is effected by means of an oxidizing agent selected from the group consisting of hydrogen`peroxide, sodium peroxide, barium peroxide, chlorine, hypochlorite.

BERNARD SUTRO GREENSFELDER. MONROE EDWARD SPAGHT. CLYDE HAROLD BRITTEN. 

